Among the first prerequisites for a powder laundry detergent is that it must dissolve completely in a relatively short time interval under whatever wash temperature and agitation conditions are employed in the wash cycle chosen by the consumer. Undissolved detergent not only fails to provide cleaning benefits, but also may become entrapped in the laundry articles and remain behind as a residue either in the machine or on the garments themselves. The problem of dispersion and solubilization in the wash cycle are made worse under conditions of cold water washing especially below about 50.degree. F. and restricted or gentle agitation conditions. Both lower wash temperatures and milder agitation conditions are becoming ever increasing factors in today's washloads as both energy conservation and increased use of highly colored, delicate fabrics lead to wash conditions that make powders difficult to dissolve.
A particular problem arises with the use of high density laundry detergent powders; i.e., those with bulk densities 650 g/L or greater. Denser powders such as those of 800 g/L or higher are even more problematic. While these powders provide consumers the benefit of concentration and lower dosages, the processes required to produce high densities leave little or no void space in the detergent powder. See, for example, U.S. Pat. No. 5,133,924 which describes a process that reduces the intraparticle porosity so that void space is substantially decreased. These highly concentrated powders can prove difficult to dissolve since the powder has little or no free space to allow the entry of water necessary for dissolution. This, in turn, can result in the powder forming localized areas of gellation which remain undissolved at the end of the wash cycle and contribute to residue. Prior to the invention described herein, it does not appear that the problem of product residue has been satisfactorily resolved.
The inclusion of a non-surfactant solubility aid which is preferably a C.sub.2 -C.sub.4 alkylene oxide condensation product increases the dissolution of high density powders with low intraparticle porosity and significantly reduces the potential for residue to remain behind. It is this improvement in the dissolving property of high density powders through the incorporation of solubility aids of specific molecular weights that forms the basis for the instant invention.
Spadini et al (U.S. Pat. No. 4,490,271) discloses the use of polyethylene glycols with polyacrylates of specified molecular weights to improve the removal of clay soils.
Murphy (U.S. Pat. No. 4,379,080)discloses the use of film forming polymers such as the copolymers of acrylic and maleic acid in a zeolite built powder to provide granules with free flowing characteristics and improved solubility.
Rose (U.S. Pat. No. 4,303,557) teaches the use of copolymers of maleic anhydride and vinyl alkyl ethers for use in zeolite containing detergents resulting in improved hard water detergency and providing granules with improved physical properties particularly improved breakdown resistance and reduced dustiness.
Ferry (U.S. Pat. No. 4,276,205) teaches the use of amine oxide surfactant in combination with alkyl phenol ethoxylates and alkylene oxide condensation products such as polyethylene glycol for use in providing superior detergency in cool or cold water fabric cycles.